Back to EveryPatent.com
| United States Patent |
5,786,119
|
|
Sorriero
, et al.
|
July 28, 1998
|
Electrophotographic elements having charge transport layers containing
high mobility polyester binders
Abstract
An electrophotographic element comprising a high mobility charge transport
layer. The layer binder is a polyester according to formula I:
##STR1##
wherein Ar represents phenylene, terephthoyl, isophthoyl,
5-t-butyl-1,3-phenylene and phenylene indane;
D represents alkyl, linear or branched, or cycloalkyl, having from 4 to
about 12 carbons;
R.sup.1, R.sup.2, R.sup.7, and R.sup.8 represent H, alkyl having 1 to 4
carbon atoms, cyclohexyl, norbornyl, phenylindanyl, perfluoralkyl having 1
to 4 carbon atoms, .alpha., .alpha.-dihydrofluoroalkyl having 1 to 4
carbon atoms, and .alpha.,.alpha.,.omega.-hydrofluoroalkyl having 1 to 4
carbon atoms; and
R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.9, R.sup.10, R.sup.11, and
R.sup.12 represent, H, halo and alkyl having from 1 to about 6 carbons;
x is from 0 to 0.8; and
y is from 0 to 1.
| Inventors:
|
Sorriero; Louis Joseph (Rochester, NY);
O'Regan; Marie B. (Rochester, NY);
Borsenberger; Paul Michael (Hilton, NY)
|
| Assignee:
|
Eastman Kodak Company (Rochester, NY)
|
| Appl. No.:
|
584502 |
| Filed:
|
January 11, 1996 |
| Current U.S. Class: |
430/58.3; 430/58.75; 430/59.6; 430/96 |
| Intern'l Class: |
G03G 005/047 |
| Field of Search: |
430/58,59,96
|
References Cited
U.S. Patent Documents
| 3615414 | Oct., 1971 | Light | 430/56.
|
| 4072520 | Feb., 1978 | Rochlitz et al.
| |
| 4175960 | Nov., 1979 | Berwick et al.
| |
| 4840860 | Jun., 1989 | Staudenmayer et al. | 430/96.
|
| 5120627 | Jun., 1992 | Nozomi et al.
| |
| 5122429 | Jun., 1992 | Sundararajan et al.
| |
| 5130215 | Jul., 1992 | Adley et al.
| |
| 5162485 | Nov., 1992 | Odell et al.
| |
| 5232800 | Aug., 1993 | Pavlisko et al.
| |
| 5232801 | Aug., 1993 | Rule et al.
| |
| 5232802 | Aug., 1993 | Rule et al.
| |
| 5266429 | Nov., 1993 | Sorriero et al.
| |
| 5316880 | May., 1994 | Pai et al.
| |
| Foreign Patent Documents |
| 77593 | Apr., 1983 | EP.
| |
| 312469 | Apr., 1989 | EP.
| |
| 552740 | Jul., 1993 | EP.
| |
| 2-127654 | May., 1990 | JP.
| |
Other References
Borsenberger, Paul M. and David S. Weiss. Organic Photoreceptors for
Imaging Systems. New York: Marcel-Dekker, Inc. pp. 312-325, 1993.
Borsenberger, Paul M. and David S. Weiss. Organic Photoreceptors for
Imaging Systems. New York: Marcel-Dekker, Inc. pp. 190-211, 1993.
Chemical Abstracts 113:221321, 1990.
"Electron Transport in Disordered Organic Solids" by Paul M. Borsenberger
pp. 273-279, Oct. 1990.
|
Primary Examiner: Rodee; Christopher D.
Attorney, Agent or Firm: Everett; John R.
Claims
What is claimed is:
1. An electrophotographic element comprising an aggregate charge generation
layer and a charge transport layer containing a charge transport material
and a polyester binder: wherein
(a) the polyester binder is selected from a group consisting of
poly{4,4'-isopropylidenebisphenylene terephthalate-co-azelate};
poly{4,4'-isopropylidenebisphenylene
terephthalate-co-isophthalate-co-azelate};
poly{4,4'-isopropylidenebisphenylene-co-4,4'-hexafluoroisopropylidene
bisphenylene terephthalate-co-azelate};
poly{4,4'-hexafluoroisopropylidenebisphenylene terephthalate-co-azelate};
poly{hexafluoroisopropylidenebisphenylene
terephthalate-co-isophthalate-co-azelate} and
poly{4,4'-isopropylidenebisphenylene isophthalate-co-azelate}; and
(b) the charge transport material is selected from the group consisting of
(i) a mixture of tri-tolylamine;
1,1-bis(di-4-tolylamino-phenyl)cyclohexane; and
diphenylbis-(4-diethylaminophenyl)methane and (ii) a mixture of
3,3'-(4-p-tolylaminophenyl)-1-phenylpropane and
diphenylbis-(4-diethylaminophenyl)methane.
2. The electrophotographic element of claim 1 wherein the polymeric binder
is poly{4,4'-isopropylidene bisphenylene-co-4,4'-hexafluoroisopropylidene
bisphenylene terephthalate-co-azelate}; and the charge transport material
is a mixture of tri-tolylamine; 1,1-bis(di-4-tolylaminophenyl)cyclohexane;
and diphenylbis-(4-diethylaminophenyl)methane.
3. The electrophotographic element of claim 1 wherein the polymeric binder
is poly{4,4'-isopropylidene bisphenylene-co-4,4'-hexafluoroisopropylidene
bisphenylene terephthalate-co-azelate}; and the charge transport material
is a mixture of 3,3'-(4-p-tolylaminophenyl)-1-phenylpropane and
diphenylbis-(4-diethylaminophenyl)methane.
4. An electrophotographic element according to claim 1 wherein:
(a) the polyester binder is selected from the group consisting of:
poly{4,4'-isopropylidenebisphenylene-co-4,4'-hexafluoroisopropylidene
bisphenylene terephthalate-co-azelate};
poly{4,4'-hexafluoroisopropylidenebisphenylene terephthalate-co-azelate}
and
poly{hexafluoroisopropylidenebisphenylene
terephthalate-co-isophthalate-co-azelate}.
Description
CROSS REFERENCE TO RELATED APPLICATION
Reference is made to and priority claimed from U.S. Provisional Application
Ser. No. 60/002,662, filed 22 Aug. 1995, entitled ELECTROPHOTOGRAPHIC
ELEMENTS HAVING CHARGE TRANSPORT LAYERS CONTAINING HIGH MOBILITY POLYESTER
BINDERS.
1. Field of the Invention
The invention relates to electrophotographic elements.
2. Background of the Invention
Electrophotographic imaging processes and techniques have been extensively
described in both the patent and other literature, for example, U.S. Pat.
Nos. 2,221,776; 2,227,013; 2,297,691; 2,357,809; 2,551,582; 2,825,814;
2,833,648; 3,220,324; 3,220,831; 3,220,833 and many others. Generally,
these processes have in common the steps of employing a photoconductive
insulating element which is prepared to respond to imagewise exposure with
electromagnetic radiation by forming a latent electrostatic charge image.
A variety of subsequent operations, now well-known in the art, can then be
employed to produce a visible record of the electrostatic image.
A group of important electrophotographic elements used in these processes
comprise a conductive support in electrical contact with a charge
generation layer (CGL) and a charge transport layer (CTL) are known. The
concept of using two or more active layers in electrophotographic
elements, at least one of the layers designed primarily for the
photogeneration of charge carriers and at least one other layer designed
primarily for the transportation of these generated charge carriers are
sometimes referred to as multilayer or multiactive electrophotographic
elements. Patent publications disclosing methods and material for making
and using such elements include: Bardeen, U.S. Pat. No. 3,401,166 issued
Jun. 26, 1962; Makino, U.S. Pat. No. 3,394,001 issued Jul. 23, 1968;
Makino et. al. U.S. Pat. No. 3,679,405 issued Jul. 25, 1972; Hayaski et.
al., U.S. Pat. No. 3,725,058 issued Apr. 3, 1973; Canadian Patent No.
930,591 issued Jul. 24, 1973; and Canadian Patent Nos. 932,197-199 issued
Aug. 21, 1973; and British Patent Nos. 1,337,228, 1,343,671. More recent
publications include U.S. Pat. Nos. 4,701,396; 4,666,802; 4,427,139;
3,615,414; 4,175,960 and 4,082,551.
Charge transport layers have a binder in which a charge transport material
is dispersed. The key requirement for the charge transport layer is that
the photogenerated charges from the charge generation layer must not be
deeply trapped (i.e. incapable of transport) and must transit the charge
transport layer thickness in a time that is short compared to the time
between the exposure and image development steps. This sets a lower limit
for a parameter referred to as mobility or carrier drift velocity. These
parameters are interrelated as follows:
v=.mu.E
where v is the carrier drift velocity, .mu. is the mobility, and E is the
electric field. (The fields that are normally used for electrophotography
are between 2.times.10.sup.4 and 5.times.10.sup.5 V/cm.) For conditions of
practical interest, the minimum mobility is in the range of a few
multiples of 10.sup.-6 cm.sup.2 /Vs in the field range of interest.
The choice of the transport layer polymer binder is based on several
considerations: 1) it must be soluble in conventional coating solvents, 2)
it must be miscible with the intended charge transport material at high
concentrations, 3) it must be a good film former with appropriate physical
and mechanical properties, 4) it must have be highly transparent
throughout the intended region of the spectrum, and 5) it must provide for
an acceptable charge mobility.
Polymers that have found widespread application in transport layers are
limited to a few specific polycarbonates and polyesters. One polyester,
poly›4,4'-norbornylidene bisphenylene terephthalate-co-azelate!, provides
a good combination of features for the just stated considerations. However
it is relatively expensive, provides less than desirable mobility for
charge transport materials, especially mixtures of charge transport
materials.
SUMMARY OF THE INVENTION
The invention, in its broader aspects, provides an electrophotographic
element comprising a charge generation layer and a charge transport layer
having a binder according to formula I:
##STR2##
wherein Ar represents phenylene, terephthoyl, isophthoyl,
5-t-butyl-1,3-phenylene and phenylene indane;
D represents alkyl, linear or branched, or cycloalkyl, having from 4 to
about 12 carbons;
R.sup.1, R.sup.2, R.sup.7, and R.sup.8 represent H, alkyl having 1 to 4
carbon atoms, cyclohexyl, norbornyl, phenylindanyl, perfluoralkyl having 1
to 4 carbon atoms, .alpha., .alpha.-dihydrofluoroalkyl having 1 to 4
carbon atoms, and .alpha.,.alpha.,.omega.-hydrofluoroalkyl having 1 to 4
carbon atoms; and
R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.9, R.sup.10, R.sup.11, and
R.sup.12 represent, H, halo and alkyl having from 1 to about 6 carbons;
x is from 0 to 0.8; and
y is from 0 to 1.
It is an advantageous effect of at least some of the embodiments of the
invention that are relatively inexpensive, exhibits enhanced scratch
resistance and provides improved mobility for charge transport materials,
especially mixtures of charge transport materials compared to the above
mentioned prior art charge transport layer binder. Also with some
embodiments the charge transport layer can be coated at a higher dry
coverage while retaining superior sensitometric properties. This results
in extended film process lifetime.
The mobilities of charge carriers in the polyesters used in the
electrophotographic elements provided by this invention are surprising in
that they are higher than the mobilities of the same materials in similar
polyesters used in commercial electrophotographic elements. See polymer A
in the examples. There is nothing in the art that would lead us to expect
this increase in mobility since the structures of (A) and the polymers of
the invention are similar.
DETAILS OF THE INVENTION
The charge transport layer contains, as the active charge transport
material, one or more organic photoconductors capable of accepting and
transporting charge carriers generated in the charge generation layer.
Useful charge transport materials can generally be divided into two
classes. That is, most charge transport materials generally will
preferentially accept and transport either positive charges, holes, or
negative charges, electrons, generated in the charge generation layer.
The polyesters binders for the charge transport layers provided by the
present invention can be prepared using well known solution polymerization
techniques such as disclosed in W. Sorenson and T. Campbell, Preparative
Methods of Polymer Chemistry, page 137, Interscience (1968). Polymers
which were evaluated in the standard charge transport layer (CTL) for the
described multi-layer photoreceptor were all prepared by means of solution
polymerization techniques. Schotten-Baumann conditions were employed to
prepare the polyester binders as described below:
Table 1 presents polyesters that are useful.
Table 1
1. poly{4,4'-isopropylidene bisphenylene terephthalate-co-azelate (70/30)}
2. poly{4,4'-isopropylidene bisphenylene
terephthalate-co-isophthalate-co-azelate (50/25/25)}
3. poly{4,4'-isopropylidene bisphenylene-co-4,4'-hexafluoroisopropylidene
bisphenylene (75/25) terephthalate-co-azelate (65/35)}
4. poly{4,4'-isopropylidene bisphenylene-co-4,4'-hexafluroisopropylidene
bisphenylene (50/50) terephthalate-co-azelate (65/35)}
5. poly{4,4'-hexafluoroisopropylidene bisphenylene terephthalate-co-azelate
65/35)}
6. poly{hexafluoroisopropylidene bisphenylene
terephthalate-co-isophthalate-co-azelate (50/25/25)}
7. poly{4,4'-isopropylidene bisphenylene isophthalate-co-azelate (50/50)}
The thickness of the charge transport layer may vary. It is especially
advantageous to use a charge transport layer which is thicker than that of
the charge generation layer, with best results generally being obtained
when the charge transport layer is from about 2 to about 200 times, and
particularly 10 to 40 times, as thick as the charge generation layer. A
useful thickness for the charge generation layer is within the range of
from about 0.1 to about 15 microns dry thickness, particularly from about
0.5 to about 6 microns.
The charge generation layer is generally made up of a charge generation
material dispersed in an electrically insulating polymeric binder. The
charge generation layer may also be vacuum deposited, in which case no
polymer is used. Optically, various sensitizing materials such as spectral
sensitizing dyes and chemical sensitizers may also be incorporated in the
charge generation layer. Examples of charge generation material include
many of the photoconductors used as charge transport materials in charge
transport layers. Particularly useful photoconductors include
titanyltetrafluorophthalocyanine, described in U.S. Pat. No. 4,701,396,
bromoindiumphthalocyanine, described in U.S. Pat. No. 4,666,802 and U.S.
Pat. No. 4,427,139, the dye-polymer aggregate described in U.S. Pat. Nos.
3,615,374 and 4,175,960, and perylenes or selenium particles described in
U.S. Pat. No. 4,668,600 and U.S. Pat. No. 4,971,873. An especially useful
charge generation layer comprises a layer of heterogeneous or aggregate
composition as described in Light, U.S. Pat. No. 3,615,414 issued Oct. 26,
1971.
Charge generation layers and charge transport layers in elements of the
invention can optionally contain other addenda such as leveling agents,
surfactants, plasticizers, sensitizers, contrast control agents, and
release agents, as is well known in the art.
The multilayer photoconductive elements of the invention can be affixed, if
desired, directly to an electrically conducting substrate. In some cases,
it may be desirable to use one or more intermediate subbing layers between
the conducting substrate to improve adhesion to the conducting substrate
and/or to act as an electrical barrier layer between the multi-active
element and the conducting substrate as described in Dessauer, U.S. Pat.
No. 2,940,348.
Electrically conducting supports include, for example, paper (at a relative
humidity above 20 percent); aluminum-paper laminates; metal foils such as
aluminum foil, zinc foil, etc.; metal plates, such as aluminum, copper,
zinc, brass and galvanized plates; vapor deposited metal layers such as
silver, chromium, nickel, aluminum and the like coated on paper or
conventional photographic film bases such as cellulose acetate,
polystyrene, poly(ethylene terephthalate), etc. Such conducting materials
as chromium, nickel, etc., can be vacuum deposited on transparent film
supports in sufficiently thin layers to allow electrophotographic elements
prepared therewith to be exposed from either side of such elements.
In preparing the electrophotographic elements of the invention, the
components of the charge generation layer, or the components of the charge
transport layer, including binder and any desired addenda, are dissolved
or dispersed together in an organic solvent to form a coating composition
which is then solvent coated over an appropriate underlayer, for example,
a support or electrically conductive layer. The liquid is then allowed or
caused to evaporate from the mixture to form the charge generation layer
or charge transport layer.
Suitable organic solvents include aromatic hydrocarbons such as benzene,
toluene, xylene and mesitylene; ketones such as acetone, butanone and
4-methyl-2-pentanone; halogenated hydrocarbons such as dichloromethane,
1,1,2-trichloroethane, chloroform and ethylene chloride; ethers including
ethyl ether and cyclic ethers such as dioxane and tetrahydrofuran; other
solvents such as acetonitrile and dimethylsulfoxide; and mixtures of such
solvents. The amount of solvent used in forming the binder solution is
typically in the range of from about 2 to about 100 parts of solvent per
part of binder by weight, and preferably in the range of from about 10 to
50 parts of solvent per part of binder by weight.
In the coating compositions, the optimum ratios of charge generation
material or of both charge generation material and charge transport
material, to binder can vary widely, depending on the particular materials
employed. In general, useful results are obtained when the total
concentration of both charge generation material and charge transport
material in a layer is within the range of from about 0.01 to about 90
weight percent, based on the dry weight of the layer. In a preferred
embodiment of a multiple layer electrophotographic element of the
invention, the coating composition contains from about 0 to about 40
weight percent of charge transport agent and from 0.01 to about 80 weight
percent of charge generation material.
The initial image forming step in electrophotography is the creation of an
electrostatic latent image on the surface of a photoconducting insulator.
This can be accomplished by charging the element in the dark to a
potential of several hundreds volts by either a corona or roller charging
device, then exposing the photoreceptor to an imagewise pattern of
radiation that corresponds to the image that is to be reproduced.
Absorption of the image exposure creates free electron-hole pairs which
then migrate through the charge transport layer under the influence of the
electric field. In such a manner, the surface charge is dissipated in the
exposed regions, thus creating an electrostatic charge pattern.
Electrophotographic toner can then be deposited onto the charged regions.
The resulting image can be transferred to a receiver and fused.
EXAMPLES
The following examples are presented to further illustrate the useful
mobility of charges through charge transport layers comprising polyesters
according to the invention. Comparative examples, using a commercially
used polyester binder in the charge transport layers, are presented to
show that polyesters according to the invention provide improved charge
carrier mobilities.
Comparative Example 1
Prior art polymer A binder in charge transport layer
Electrophotographic elements were prepared using, as a support, 175 micron
thick conductive support comprising a thin layer of nickel on poly
(ethylene terephthalate) substrate to form an electrically conductive
layer. A charge generation layer of amorphous selenium, about 0.3 microns
thick, was vacuum deposited over the nickel layer. A second layer (CTL)
was coated onto the CGL at a dry coverage of 1.2 g/ft.sup.2 with a doctor
blade. The CTL mixture comprised 60 wt %
poly›4,4'-(2-norbornylidene)bisphenylene terephthalate-co-azelate-(60/40)!
(polymer A), 19.75 wt % 1,1-bis-›4-(di-4-tolylamino)phenyl!cyclohexane
›CTM 1!, 19.5 wt % tri-(4-tolyl)amine ›CTM 2!, and 0.75 wt %
diphenylbis-(4-diethylaminophenyl)methane. The CTL mixture was prepared at
10 wt % in a 70/30 (wt/wt) mixture of dichloromethane and methyl acetate.
A coating surfactant, DC510, was added at a concentration of 0.024 wt % of
the total CTL mixture.
Polymer A is used in the charge transport layer of many commercially
available electrophotographic elements. The solvents 70:30
dichloromethane:methyl acetate, toluene, and 1,1,2-trichloroethane were
variously used in the following all of the examples herein. The choice of
solvent was found to have little or no effect on the resulting element.
The mobility measurements were made by conventional time-of-flight
techniques (Borsenberger and Weiss, Organic Photoreceptors for Imaging
Systems, Marcel Dekker Incorporated, N.Y., 1993, page 280). By this
method, the displacement of a sheet of holes, created in the .alpha.-Se
charge generation layer, is time-resolved. The exposures were of 440 nm
radiation derived from a dye laser. The exposure duration was 3 ns. The
photocurrent transients were measured with a transient digitizer
(Tektronix model 2301). The mobilities were determined from the
conventional expression
.mu.=L.sup.2 /t.sub.0 V,
where L is the sample thickness, t.sub.0 is the transient time of the
photogenerated charge sheet and V is the applied voltage.
The mobilities are shown in Tables 2 and 3.
Example 1
An electrophotographic element was prepared as in comparative example 1,
except that the binder was polymer 1, Table 1, and the CTL mixture was
prepared at 8 wt % in a 70/30 (wt/wt) mixture of dichloromethane and
1,1,2-trichloroethane. A coating surfactant, DC510, was added at a
concentration of 0.024 wt % of the total CTL mixture.
Example 2
An electrophotographic element was prepared as in comparative example 1,
except that the binder was polymer 2, Table 1, and the CTL mixture was
prepared at 10 wt % in an 80/20 (wt/wt) mixture of dichloromethane and
methyl acetate. A coating surfactant, DC510, was added at a concentration
of 0.024 wt % of the total CTL mixture.
Example 3
An electrophotographic element was prepared as in comparative example 1,
except that the binder was polymer 3, Table 1, and the CTL mixture was
prepared at 10 wt % in an 80/20 (wt/wt) mixture of dichloromethane and
methyl acetate. A coating surfactant, DC510, was added at a concentration
of 0.024 wt % of the total CTL mixture.
Example 4
An electrophotographic element was prepared as in comparative example 1,
except that the binder was polymer 4, Table 1.
Comparative Example 2
An electrophotographic element was prepared as in comparative example 1,
except that the charge transport material was 40 wt. % CTM 1, and the CTL
mixture was prepared at 10 wt. % in dichloromethane.
Comparative Example 3
An electrophotographic element was prepared as in comparative example 2,
except that the charge transport material was 40 wt. % CTM 2.
Example 5
An electrophotographic element was prepared as in comparative example 1,
except that the binder was polymer 2, Table 1 and the charge transport
material mixture was composed of 20 wt. % CTM 1 and 20 wt. % CTM 2. The
CTL mixture was prepared at 10 wt. % in a mixture of 80 wt. %
dichloromethane and 20 wt. % methyl acetate.
Example 6
An electrophotographic element was prepared as in example 5, except that
the charge transport material was 40 wt. % CTM 2.
Example 7
An electrophotographic element was prepared as in example 5, except that
the charge transport material mixture was composed of 12.5 wt. % CTM 1 and
12.5 wt. % CTM 2.
Example 8
An electrophotographic element was prepared as in example 5, except that
the charge transport material was 25 wt. % of CTM 1.
Example 9
An electrophotographic element was prepared as in example 5, except that
the charge transport material was 25 wt. % of CTM 2.
Example 10
An electrophotographic element was prepared as in Example 7, except that
the binder is polymer 1, Table 1, and the CTL mixture was made up at 8 wt.
% in a 70/30 wt./wt. mixture of dichloromethane and 1,1,2-trichloroethane.
Example 11
An electrophotographic element was prepared as in Example 10, except that
the charge transport material was 25 wt. % of CTM 2.
Example 12
An electrophotographic element as prepared in Example 10, except that the
binder is polymer 7, Table 1 and the charge transport material mixture was
15 wt. % of CTM 1 and 15 wt. % of CTM 2. The CTL mixture was prepared at a
concentration of 10 wt. % in dichloromethane.
Example 13
An electrophotographic element was prepared as in Example 12, except that
the charge transport material was 30 wt. % of CTM 1.
Example 14
An electrophotographic element was prepared as in Example 12, except that
the charge transport material was 30 wt. % of CTM 2.
TABLE 2
______________________________________
Example CTL Polymer Binder*
Mobility (cm.sup.2 /Vs)
Field (V/cm)
______________________________________
Comparative
Polymer A 3.4 .times. 10.sup.-6
2.5 .times. 10.sup.5
Example 1
(prior art)
Example 1
1 7.0 .times. 10.sup.-6
2.5 .times. 10.sup.5
Example 2
2 9.7 .times. 10.sup.-6
2.5 .times. 10.sup.5
Example 3
3 6.0 .times. 10.sup.-6
2.5 .times. 10.sup.5
Example 4
4 6.8 .times. 10.sup.-6
2.5 .times. 10.sup.5
______________________________________
*Numbers in this column refers to Table 1 polymers
The data in Table 2 indicates that the charge transport layers of Examples
1, 2, 3 and 4 showed greater mobilities than the charge transport layer of
Comparative Example 1.
At a field of 2.5.times.10.sup.5 V/cm, comparative Example 1 containing the
binder of the prior art exhibited a mobility of 3.4.times.10.sup.-6
cm.sup.2 /Vs. At the same field strength, utility example containing
polymer 2 of Table 1 showed greater mobility, 9.7.times.10.sup.-6 cm.sup.2
/Vs.
TABLE 3
______________________________________
Total
CTM 1 CTM 2 CTM
Binder conc. conc. conc. Mobility
Example polymer* (wt. %) (wt. %)
(wt. %)
(.times. 10.sup.-6
______________________________________
cm.sup.2 /Vs)
Comparative
Polymer A
20 20 40 3.4
Example 1
Comparative
Polymer A
40 0 40 5.0
Example 2
Comparative
Polymer A
0 40 40 5.6
Example 3
Example 5
2 20 20 40 9.7
Example 6
2 0 40 40 6.5
Example 7
2 12.5 12.5 25 0.20
Example 8
2 25 0 25 0.094
Example 9
2 0 25 25 0.10
Example 10
1 12.5 12.5 25 0.45
Example 11
1 0 25 25 0.7
Example 12
7 15 15 30 0.9
Example 13
7 30 0 30 0.57
Example 14
7 0 30 30 0.5
______________________________________
*Numbers in this column refers to Table 1 polymers
The mobilities of charge transport materials (CTM) in elements of Polymers
A, were higher for charge transport layers containing a single charge
transport material than for layers containing a mixture of materials. This
is a well recognized phenomenon in the art.
In the case of polymer 2 of Table 1, we observed an exception to the prior
art phenomenon, as is illustrated in Table 3. Examine mobilities provided
by polymer 2 at 25 percent loading of CTM (compare Example 7 to Examples 8
and 9) or at 40 percent loading of CTM (compare Examples 5 and 6). Both
examples show consistently higher mobilities for charge transport material
mixtures than for either of the single CTMs. This is novel and unexpected.
The prior art teaches that the mobility of carriers in layers containing
only one charge transport material will be higher than in the charge
transport layer containing a mixtures of charge transport materials.
While specific embodiments of the invention have been shown and described
herein for purposes of illustration, the protection afforded by any patent
which may issue upon this application is not strictly limited to a
disclosed embodiment; but rather extends to all modifications and
arrangements which fall fairly within the scope of the claims which are
appended hereto:
Top